Electron tube



May 24, 1932. B., F. MIESSNER ELECTRON TUBE Filed Feb. 25, 1930 2 Sheets-Sheet 1 0 v E W 7 mm 6 MM M1 y Q B. F. MIESSNER 1,859,454

ELECTRON TUBE Filed Feb. 25, 1930 2 Sheets-Sheet 2 641m m l Patented May 24, 1932 UNITED STATES I PATENT orric" I BENJAMIN r. MIEssNER, or sHoRT HILLS, NEW JERSEY, ssrsno To MIESSNER. I N- VENTIONS ING, or SHORT HILLS, NEW JERSEY, A CORPORATION OF NEW JERSEY- ELECTRON TUBE Application filed'lebruary 25, 1930. Serial No. 431,121.

This invention relates to space discharge devices of thermionic type and particularly to the type in which the cathodeis a unipotential cathode. This structure usually embodies a conductive thimble indirectly heated, chiefly by radiation and conduction from a heater element energized by alternating current. I i

The primary object of my invention is to minimize or substantially eliminate hum introduced into the output circuit of the tube by fluctuating temperatures, voltages or currents within the heater element when the same is energized by alternating current.

Other objects of my invention are the pro duction of rigid structures in which varlous spacings of the elements will be maintained constant throughout the life of the tubeas will be more particularly pointed out as the description thereof is developed in the following specification. i

I have discovered that in this type of tube, having an indirectly heated cathode, one of the chief sources of hum in the output of the tube is due to the magnetic field of the heater current. Other features contributing to. hum are the leakage of heater current through the insulating material into the cathode, and voltage effects across segments of the heater element itself, as well as voltage effects between the heater element and the cathode thimble. Tubes of present-clay manufacture utilize a straight or helically coiled wire extending through the cathode thimble with or without an intervening insulator toprevent contact with the cathode thimble, or a hairpin type heater with straight parallel legs extending through a cylindrical insulator having two holes longitudinally throughout and parallel to its axis.

The heater wire in this latter type is round and the separation between the two sides or legs of the hair-pin is about the diameter of the cylindrical insulator, which fits snugly into the cathode thimble.

The separation of the heater legs in such a type of cathode produces a considerable magnetic field, incompletely neutralized, which reaches out into the electron stream near the cathode surface and there causes a chan e of direction in the flow of the electrons to the plate periodically with the rise and fall of the ma netic field following the alternation of the eating current flow therethrough. This change inthe magnetic field at the surface of the cathode is the primary element varying in the plane bisecting both heater legs the distance between a legand the nearest cathode wall. portion is about equal to the separation between the heater legs so that near this plane thereis considerable unneutralized field at the cathode surface. In areas on the cathode subtantially parallel to this plane there is substantial neutralization between the magnetic fields individually produced by the legs.

I have developed two fundamental features which I have includedin the structures to be described hereinafter for minimizing the'fiuctuations in the magneticfield at the surface of the cathode. The first is the feature of maintaining the centers of the legs as close together as possible, thereby producing more nearly perfect neutralization between the magnetic fields thereof, and the second is the location of the emissive surface alongpoints on the cathode thimble wherein most complete neutralization of the magnetic fields from the two legs of the heater element is obtained.

Referring to the drawings, in which like reference characters have been used throughout insofar as possible, Fig. 1 diagrammatically illustrates a complete electron tube of my improved form. I

Fig. 2 shows the tube of Fig. 1 partly in section to disclose the relationship of the cathode connection and the connections to the heater element in relationship to the grid and plate leads.

Fig.3 diagrammatically illustrates a crosssection of the tube of Fig.1 on the line 33 of Fig. 2. j

" Fig.6.

' lead-in wire to the grid of the tube.

accomplished since the cathode lead-in is usu-,

Fig. 4 is a cross sectionof a cathode of in improved form; v p

Fig. 4A graphically illustrates the hum outputof an electron tube with change of position of electron emissive material upon the surface of a cathode of the type shown in Fig. 4;

Fig. 5, is a cross section of a modified form of my invention;

Fig. 5A graphically illustrate-s the hum output of an electron tube-with change of' position of electron emissive material upon the surface of a cathode of the type of Fig. 5; v

Fig.6 is a modification of the type of cathode shown'in Fig.5; i

Fig. 6A graphically illustrates the hum output of an electron tube with change ofposition of electron emissive material upon the surface of a cathode of the type shown in Referring to Figs. 1 and 2, 1 designates a base having five prongs designated 2 to 6 respectively, such as employed in the standard base of heater type tubes of present-day manufacture. This base carries a glass envelope 7 preferably evacuated and within. which there is a stem 8. Upon this stem 8 there is rigidly mounted an anode 9 either cylindrical or oblong in cross-section surrounding a grid 10 and a cathode 11. The cathode is providedwith two heater connections 12 and 12' securely mounted within the stem 8 and in continuation of lead-in wires 13 and 13, which in turn are connected to the. socket pins .3 and 4 respectively. The

cathode thimble is provided with a connec-- tion 14 sealed through the stem 8 and in continuation of a lead-in wire 15 which in turn is connected to prong 5. v

In these figures it will be noted that the cathode lead-in 15 is disposed between the lead-ins 12 and 12 to the heater'element-on. the one side and the lead-in 10 to the grid on the other side. This feature is to eliminate insofar as possible any induction in the This is ally grounded and acts as a shield bet-ween these elements. o l

The cathode thimble itself may either be cylindrical, nearly elliptical or rectangular as shown in Figs. 4, 5 and 6, details of the description of which follows hereinafter.

In sucha cathode structure the heater element is so arranged within the cathode thimble that the bend of the heater element does not protrude from the upper end of the cathode thimble, and I have found that a safe distance below the end of the cathode thimble for the bend in a hair-pin heater element is approximately .06 inch, as an example of one'of the tubes I have constructed in accordance with the features of my invention. The heater wires themselves at the bottom of the thimble should be as short as possible and connected to rugged supporting members of large heat carrying capacity so that substantially no emission occurs from' legs 19 and 20 of the heaterv element are c passed. The insulating member 16 is of a type commonly used in slowheater cathode types of tubes available on the market of the present day, and in which the holes 17 and 18 are spaced at'a distance of approximately 0.02 inches. Surrounding the insulating member 16,I have provided a cathode thimble 21 of nickel, approximately. 0.001 inches thick and about 0.05 inchdiameter.

p In. examining the electrical constants of a cathode of this structure, I have determined that the fluctuating components present in the plate circuit of a tube having a cathode of such a structure are due to varying actions of the magnetic field upon small portions of electron emissive material distributed about the surface'of the cathode thimble 21.

In Fig. 4A, I have graphically developed as curves 22 and 23 in polar coordinates the hum in equivalent volts developed in the plate circuit of a tube having a cathode of this character as a small amount of electron emissive material is progressively moved around the cathode. An analysis of curves-22 and 23 clearly illustrates that nearthe plane YY on the cathode no appreciable hum is developed in the plate circuit of the tube. However, it will also be noticed that as the electron emissive material is moved away from the axis YY, to other parts of the cathode surface, hum devlops with a maximum being reached when the electron emission material lies parallel to-the plane bisecting the spacebetween the legs 19 and 20 of the hair-pin heater. This isdue to the differing distances between the emissive material and the two heater legs 19 and 20. Therefore as one simple form of my invention I propose to coat thecathode thimble 21 shown in Fig. 4 with strips of electron emission material as indicated at 24 and 25. It will be noted herein that I have located the electron emissive material at those portions of the cathode wherein the hum curves 22 and 23 of Fig. 4A do not depart appreciably from the zero polar ordinate of hum.

In Fig. 5 I have shown a cathode builtup of a central thin sheet of insulating material 26 of mica or like heat resisting material, an 7 insulator at high temperatures, upon opposite sides of which are placed fiat ribbons 27 and 28 of tungsten or molybdenum wire about 0.001 inches thick and 0.020 inches wide, forming the legs of the heater element. Upon the outer sides of the heater legs 27 and 28 I have provided insulating strips of mica 29 and 80, or like insulating material, the manner of manufacture being described with reference to Fig. 7. Upon'the outside of these insulating strips 29. and 30, there is placed an elliptical cathode thimble 31 sufficiently thick to maintain the insulating elements 26, 29 and 30 and the heater ribbons 27 and 28 in a fixed rigid condition at all temperatures. An investigation of the bum developed within the plate circuit of a vacuum tube employing a cathode of this character is shown in Fig. 5A, wherein the curves 32 and 33 illustrate the hum as the electron emissive material is moved around.

over the surface of the cathode thimble 31. Likewise in this structure it will be seen that near the plane'YY there is substantially no hum developed in the. output current of the tube utilizing such a cathode structure. In this structure therefore, I employthe electron emissive material at the narrow ends of the oblong shape as shown at 34 and 35 thus placing the material as far remote from any magnetic influence as possible.

The graphs in this figure and those ofFigs. 6A are upon a scale enlarged by many times the scale of that of Fig. 4A in order to render the same visible on a drawing of this size. In

the actual structures built the maximum hum developed by the structures of Figs. 5 and 6 was substantially one fiftieth of that of the structure of Fig. 4.

Referring to Fig. 5A it will be noted that should any emissive material be spilled or creep over the surface of the cathode 31 during the manufacture or use of the tube, there will be no appreciable hum developed in the output circuit of the tube due to the more complete neutralization of the magnetic fields of the two legs 27 and 28 of the bifurcated or U shaped ribbon heater as compared with a similarly bent round-wire heater of like electric properties and like minimum distance between the inner portions of its legs. This neutralization is accomplished because the centers of the elements 27 and 28 are extremely close together and when the distance between the centers of these elements is compared to the distance therefrom of any electron emissive material, one might state that the electron emissive material is approximately equi-distant from the legs of the heater element.

In Fig. 6 I'have shown a modified form of the structure shown in Fig. 5, in which the insulating elements 29 and 30 of Fig. 5 have been replaced by grooved isolantite or like material members 39 and 40, the grooves of which closely surround the legs 27 and 28 of the U-shaped ribbon heater element. Around this entire structure, there is placed a rectangular cathode thimble 41.

In Fig. 6A, I have shown the effect of v cally identical with those illustrated in Fig- 5A with reference to the structure shown'in Fig. 5. I therefore coat the ends of the rectangular structure as .shown at 4:4 and 45 With electron emissive material.

' In each of the structures shown the uncoated surface of the cathode thimble should be of a composition that does not emit electrons at operating temperatures or it should have an emission so slight in comparison to the emissive character of the coating that the electrons coming therefrom are negligible in comparison to those produced by the emissive coating. I

As one example of a tube of my invention, I have employed a cathode of the type shown in Fig. 5 in an electrode structure" identical with that of the standard type 227 available on the market at the present time, in which the length of the cathode structure as shown in Fig. 2 was .625 inches, the Width thereof as shown in Fig. 5 was 0.12 inches and the thickness thereof as shown in Fig. 5 was .025 inches. l he ribbon heater element was 0.001 inches thick, 0.020 inches wide and 1.5 inches long of tungsten having a resistance of about 1.25 ohm. l/Vhen this heater element was. supplied with alternating current of 2 volts, the tube reached normal operating conditions after a period of about'15 seconds.

While I have shown'three individual structures and have given dimensions for particular examples of tubes embodying my invention,I am not to be limited thereby, since a tube in which the electron emissive material is placed only at points of substantially neutralized magnetic field, or cathodes having,

electron emissive materialplaced on a surface substantially parallel to the plane bisecting both heater legs come within the scope of my invention as illustrated inthe foregoing figures and defined in the appended claims.

Having thus described my invention, what I claim is: i

1. In an electron tube, the combination of a cathode, acontrol electrode surrounding said cathode and an anode surrounding said control electrode and cathode, said cathode consisting of a conductive thimble, a hairpin heater element extending axially within said thimble and being insulated therefrom, and an electron emissive substance on the exterior of said thimble, said electron emissive material being located at only portions of said cathode thimble substantially equidistant'from both legs of said heater element.

2. .A cathode for electron tubes, comprising a conductive thimble, a hair-pin heater element extending axially within said thimble and being insulated therefrom, an electron emissive substance-on the exterior of said thimble, said electron emissive materi'al'being located at only portions of said cathode thimble substantially equidistant from both legs of said heater element.

3. A cathode for electron tubes, comprising a conductive thimble, a hair-pinheater element within said thimble and'insulated therefrom, the legs of said heater element lying in a plane coinciding with one diameter of said thimble, and an electron emissive material on the surface'of said thimble substantially restricted to a surface parallel to said lane. V a

4. A cathode for electron tubes, comprising a conductive thimble, a hair-pin heater element extending axially within said thim ble and being insulated therefrom, said thimble having a cross-section having two normal dimensions, the legs of said heater lying in a plane pertaining to one of said dimensions,

and an electron emissive material on surface portions only of said thimble substantially perpendicular to the other of said dimensions of said thimble 5. A cathode for electron tubes, comprising a conductive thimble, ahair-pin heater element extending axially within saidthim ble and being insulated therefrom, said thimble having a cross-section having two normal diameters, the legs of said heater lying in a plane containing one ofsaid diameters and an electron emissive material on surface portions only of said thimble substantially perpendicular to the other of said diameters of said thimble.

v6. In an electron tube, the combination of a cathode, a control electrode surrounding said cathode and an anode surrounding said control electrode and cathode, said cathode consisting of a conductive thimble, a bifurcated heater element formed of a flat ribbon, the legs of-which aredisposed closely'to each other and substantially axially Within said thimble and insulated therefrom, and an electron emissive substance on the exterior of said thimble, said electron emissive material being located at only portions of said cathode thimble substantially equidistant from both legs of saidheater element.

7 A cathode for electron tubes, comprising a conductive thimble, a bifurcated heater element formed of a flat ribbon, the legs of which are disposed closely to each other and substantially axially within said thimble and insulated therefrom, and an electron emissive substance on the exterior of said thimble, said electron emissive material being located at only portions of said cathode thimble substantiall'y equidistant from both legs of said heater element.

8. A cathode for electron tubes, comprising a conductive thimble, a bifurcated heater element formed of a flat ribbon, the legs of which are disposed closelyto each other and substantially axially within said thimble and insulated therefrom, the legs of said heater element being bisected by a plane passing 7 throu h one diameter of said thimble'and an vliicli are disposed closely to each other and substantially axially within said thimbleand insulated therefrom, said thimble having a cross-section having two normal dimensions,

the legs of said heater beingbisected' by a plane pertaining to one of said dimensions, and an electron emissive material on surface portions only of said thimble substantially perpendicular to the other of said dimensions of said thimble.

10. A cathode for electron tubes, compris ing a conductive thimble, a bifurcated heater element formed ofv a flat ribbon, the legs of which are disposed closely toeach other and substantially axially within said thimble and insulated therefrom, said thimble having a cross-section having two normal diameters, the legs of said vheater being'hisected by a plane containing one of said diameters and an electron emissive material on surface portions only of said thimble substantially perpendicular to the other of said diameters of said thimble. I p

'11. A cathode for electron tubes, comprising a cathode thinible,'a hair-pin heater element substantially axially extending within said thimble and being insulated therefrom, V

and an electron emissive material upon the exterior of said thimble,said thimble surface being free from electron: emissive material in a segment extending bilaterally of the plane bisecting both legs of said heater element.

12. A cathode for electron tubes, comprising a cathode thimble, a bifurcated heater element formed of a flat ribbon, the legs of which are disposed closely to each other and substantially axially Within said thimble and insulated therefrom, and an electron emissive material upon the surface of said thimble, said thimble surface being substantially free from electron emissive material in a segment extending bilaterally of the plane bisecting both legs of the heater element. J

13, A cathode for electron emission including a thimble, an electric-heater element situated interiorly of said thimble and surrounded, in operative condition, by an electromagnetic field of its own penetrating different areas on the surface of said thimble with different values of field intensity, the outer surface portions of said thimble being appreciably electron-emissive only in areas of comparatively low values of said field intensity.

1 1. A cathode for electron emission including a substantially cylindrical thimble, an elongated electric heater element situated interiorly of said thimble substantially coaxially therewith and having its sections of opposite current floW in as close proximity to each other as compatible with a safe insulation value between said sections, said heater element, when operatively energized, being surrounded by an electro-magnetic field of its own penetrating difierent segments of said thimble' with diiferent values of field intensity, the outer surface portions of said thimble being appreciably electron-emissive only in segments of comparatively low values of said field intensity.

In testimony whereof I aflix my signature. BENJAMIN F. MIESSNER. V 

